Ballast water drained from cargo ships, such as container ships, contains aquatic organisms and bacteria which inhabit ports where the ballast water is drawn. As the ships move, the organisms and bacteria are conveyed to other countries.
In serious consideration of the above background, a diplomatic conference at the International Maritime Organization (IMO) adopted the International Convention for the Control and Management of Ships' Ballast Water and Sediments to make the obligation of implementing ballast water control apply to ships built from 2009 onward.
Consequently, it is required to make it possible to drain clean ballast water that meets the International Convention for the Control and Management of Ships' Ballast Water and Sediments.
In addition, the above-mentioned Convention prescribed the ballast water discharging standard as shown in Table 1.
TABLE 1Ballast WaterItemsQuality CriteriaSizeAquatic Organisms10 unit/ml10-50 μmAquatic Organisms10 unit/m350 μm or moreIndicatorEscherichia Coli250 cfu/100 ml/MicrobesVibrio cholerae1 cfu/100 ml/(O1 and O139)Genus Enterococcus100 cfu/100 ml/
Accordingly, it is now a matter of great urgency to develop a sterilization and/or elimination technology in the ballast water to address the problems described above.
Conventionally, a technology for sterilization has been offered including injecting ozone into ballast water in parallel with injecting steam, and further generating micro bubbles of ozone to promote formation of hydroxyl radical to reduce consumption of ozone, as seen in Japanese Unexamined Patent Application No. 2004-160437 (JP).